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(11) | EP 1 693 206 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Piezoelectric inkjet printhead and method of manufacturing the same |
| (57) Provided are a piezoelectric inkjet printhead and a method of manufacturing the piezoelectric
inkjet printhead. The piezoelectric inkjet printhead is formed by bonding three single
crystal silicon substrates (100,200,300). An upper substrate (100) includes an ink
inlet (110) and a plurality of pressure chambers (120). A middle substrate (200) includes
a manifold (210) connected with the ink inlet, a plurality of restrictors (220), and
a plurality of dampers (230). A lower substrate includes a plurality of nozzles (310)
for ejecting the ink. An actuator (190) is formed on the upper substrate to apply a driving force to each of the pressure chambers for ejecting the ink. The middle substrate further includes a damping membrane (214) formed under the manifold for dampening pressure change inside the manifold, and a cavity (216) is defined in at least one of the bottom surface of the middle substrate and a top surface of the lower substrate under the damping membrane. Therefore, cross-talk can be prevented when ink is ejected since the damping membrane dampens a sudden pressure change inside the manifold, and gas generating generated when the substrates are bonded can be smoothly discharged to the outside through the cavity to prevent voids between the substrates. |
[0001] The present invention relates to an inkjet printhead, and more particularly, to a piezoelectric inkjet printhead having an improved structure for preventing cross-talk when ink is ejected, and a method of manufacturing the piezoelectric inkjet printhead.
[0002] An inkjet printer is a device for forming an image having a predetermined color onto a printing medium by ejecting ink droplets onto a desired region of the printing medium. The ilnkjet printheads can be classified into two types according to the ejecting mechanism of ink droplets: the a thermal type inkjet printhead that creates bubbles with by heating the ink heat to eject ink droplets by the expansion of the bubbles, and the a piezoelectric type inkjet printhead that includes a piezoelectric material to eject ink droplets by utilizing the pressure generated by the deformation of the piezoelectric material.
[0003] FIG. 1 shows a structure of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a manifold 2, a restrictor 3, a pressure chamber 4, and a nozzle 5 are formed in an ink flow plate 1 to form an ink path. A piezoelectric actuator 6 is installed on a top of the ink flow plate 1. The manifold 2 supplies ink from an ink reservoir (not shown) to each pressure chamber 4, and the restrictor 3 is an ink passage between the manifold 2 and the pressure chamber 4. The pressure chamber 4 receives the ink to be ejected and changes its volume in response to the operation of the piezoelectric actuator 6 to create a pressure variation for ejecting and receiving the ink. A top wall of the pressure chamber 4 bends and returns to its original shape according to the operation of the piezoelectric actuator 6. The top wall is used as a vibration plate 1a.
[0004] In operation, wWhen the vibration plate 1a is deformed by the piezoelectric actuator 6, the volume of the pressure chamber 4 decreases and the pressure of the pressure chamber 4 increases, such that ink contained in the pressure chamber 4 can be ejected to the outside through the nozzle 5. Next, when the vibration plate 1 a returns to its original shape according to the operation of the piezoelectric actuator 6, the volume of the pressure chamber 4 increases and the pressure of the pressure chamber 4 decreases, such that ink can be pulled moved back into the pressure chamber 4 from the manifold 2 through the restrictor 3.
[0005] In the conventional inkjet printhead, the ink flow plate 1 is generally formed of using a plurality of thin ceramic, metal, or synthetic plates. The thin plates are individually processed into to have shapes corresponding to the ink flow path of the ink flow pate 1, and then the thin plates are stacked and bonded to form the ink flow plate 1. In this case, since the plurality of thin plates are aligned through many operations, alignment errors increase and the manufacturing process of the inkjet printhead is complicated. The alignment errors cause non-smooth ink flow and lower the ink ejecting performance of the inkjet printhead. Particularly, since recent printheads have a highly integrated structure for high resolution, precise aligning becomes more important in the manufacturing process of the printhead. Further, the precise aligning may influence the price of the printhead.
[0006] In addition, since the thin plates of the printhead are formed of different materials using different methods, the manufacturing process of the printhead is complicated and it is difficult to bond the thin plates, thereby decreasing the yield of the printhead. Further, since the thin plates of the printhead are formed of different materials, the alignment of the thin plates may be distorted or the thin plates may be deformed according to temperature change due to different thermal expansion characteristics of the thin plates even though the thin plates are precisely aligned and bonded together in manufacturing process.
[0007] To solve these problems, a piezoelectric printhead having an improved structure has been disclosed in Korean Patent Laid-Open Publication NONo. 2003-0050477 applied by the present applicant of the present invention. The disclosed piezoelectric inkjet printhead is shown in FIGS. 2 and 3.
[0008] Referring to FIGS. 2 and 3, the piezoelectric inkjet printhead has a stacked structure formed by stacking and bonding three silicon substrates 30, 40, and 50. An upper substrate 30 includes pressure chambers 32 formed in a bottom surface to a predetermined depth and an ink inlet 31 formed through one side for connection with an ink reservoir (not shown). The pressure chambers 32 are arranged in two lines along both sides of a manifold 41 formed in a middle substrate 40. Piezoelectric actuators 60 are formed on a top surface of the upper substrate 30 to apply driving forces to the pressure chambers 32 for ejecting ink. The middle substrate 40 includes the manifold 41 connected with the ink inlet 31 and a plurality of restrictors 42 formed on both sides of the manifold 41 in connection with the respective pressure chambers 32. A barrier rib 44 is formed in the manifold 41 to prevent cross-talk between the pressure chambers 32 arranged in two lines along both sides of the manifold 41. The middle substrate 40 further includes dampers 43 formed therethrough in a vertical direction at positions corresponding to the pressure chambers 32 formed in the upper substrate 30. A lower substrate 50 includes nozzles 51 connected with the dampers 43.
[0009] As described above, the piezoelectric inkjet printhead shown in FIGS. 2 and 3 is configured by stacking the three substrates 30, 40, and 50. Thus, since the number of the substrates of the piezoelectric inkjet printhead shown in FIGS. 2 and 3 is smaller than that of the conventional piezoelectric inkjet printhead, thereby simplifying the manufacturing process of the piezoelectric inkjet printhead is simpler and decreasing the aligning errors are reduced when the substrates are stacked.
[0010] However, when a vibrating plate 33 above the pressure chambers 32 is deformed by the operation of the piezoelectric actuators 60, ink is ejected through the nozzles 51 and at the same time the ink flows reversely into the manifold 41 through the restrictors 42. Due to this reverse flow of the ink, the pressure of in the manifold 41 increases non-uniformly. When the vibrating plate 33 returns to its original shape, the ink contained in the manifold 41 suddenly flows into the pressure chambers 32 through the restrictors 42. Thus, the pressure of the manifold 41 decreases non-uniformly. Since the pressure inside the manifold 41 changes suddenly and non-uniformly as described above, the pressure chambers 32 adjacent to the manifold 41 are affected by the pressure change of the manifold 41, thereby causing cross-talk between the pressure chambers 32. Meanwhile, although the barrier rib 44 formed in the manifold 41 can prevent cross-talk between the two pressure chamber lines arranged along both sides of the manifold 41, the barrier rib 44 cannot prevent cross-talk between the pressure chambers 32 of each pressure chamber line.
[0011] If cross-talk occurs when ink is ejected as described above, ink ejecting speed and volumes of ink droplets vary undesirably.
[0012] FIG. 4 shows a speed of ink ejected through a single nozzle in comparison with a speed of ink ejected through a plurality of nozzles in the piezoelectric inkjet printhead depicted in FIGS. 2 and 3.
[0013] Referring to FIG. 4, when ink is ejected through a single nozzle as shown on in the left side of FIG. 4, the ejected ink droplet reaches a desired position indicated by a solid line since cross-talk between nozzles does not occur almost at all. However, when ink is ejected through a plurality of nozzles as shown on in the right side of FIG. 4, the ejected ink droplets are not ondo not reach a desired position indicated by a solid line due to cross-talk between the nozzles. That is, the ink ejecting speed of a single nozzle is different from the ink ejecting speed of a plurality of nozzles.
[0014] As described above, if cross-talk occurs when ink is ejected, ink cannot be ejected uniformly and thus printing quality decreases.
[0015] According to an aspect of the present invention, there is provided a piezoelectric inkjet printhead including: an upper substrate including an ink inlet therethrough for allowing inflow of ink and a plurality of pressure chambers in a bottom surface for containing the ink to be ejected; a middle substrate bonded to the bottom surface of the upper substrate, the middle substrate including a manifold formed in a top surface in connection with the ink inlet, a plurality of restrictors connecting the manifold to respective one ends of the pressure chambers, and a plurality of dampers formed therethrough at positions corresponding to respective opposite ends of the pressure chambers; a lower substrate bonded to a bottom surface of the middle substrate, the lower substrate including a plurality of nozzles formed therethrough at positions corresponding to the plurality of dampers for ejecting the ink; an actuator formed on the upper substrate to apply a driving force to each of the pressure chambers for ejecting the ink, wherein the middle substrate further includes a damping membrane formed under the manifold for dampening a pressure change inside the manifold, and a cavity is defined in at least one of the bottom surface of the middle substrate and a top surface of the lower substrate under the damping membrane.
[0017] The cavity may extend to an edge of the at least one of the bottom surface of the middle substrate and the top surface of the lower substrate for communicating with an outside. The cavity may have substantially the same width as the manifold or have a width larger than the manifold.
[0018] The manifold may be elongated in one direction, and the pressure chambers may be arranged in two lines along both sides of the manifold. In this case, a barrier rib may be formed in the manifold along a length direction of the manifold, and a supporting rib may be formed in the cavity along a length direction of the cavity in correspondence with the barrier rib.
[0019] According to another aspect of the present invention, there is provided a method of manufacturing a piezoelectric inkjet printhead, the method including: preparing an upper substrate, a middle substrate, and a lower substrate that are formed of silicon wafers; finely processing the upper substrate finely to form an ink inlet allowing inflow of ink and a plurality of pressure chambers containing the ink to be ejected; finely processing the middle substrate finely to form a manifold in a top surface of the middle substrate in connection with the ink inlet, a plurality of restrictors connecting the manifold to respective one ends of the pressure chambers, and a plurality of dampers through the middle substrate at positions corresponding to respective opposite ends of the pressure chambers; finely processing the lower substrate finely to form a plurality of nozzles ejecting the ink therethrough; sequentially stacking and bonding the lower substrate, the middle substrate, and the upper substrate; and forming a piezoelectric actuator on the upper substrate, the piezoelectric actuator providing a driving force for ejecting the ink, wherein at least one of the processing of the middle substrate and the processing of the lower substrate includes forming a cavity in at least one of a bottom surface of the middle substrate and a top surface of the lower substrate to a predetermined depth, and simultaneously forming a damping membrane between the manifold and the cavity to a predetermined thickness for dampening a pressure change inside the manifold.
[0021] The cavity may extend to an edge of at least one of the silicon wafers forming the middle substrate and the lower substrate for communicating with an outside. The cavity may have substantially the same width as the manifold or have a width larger than the manifold.
[0022] Each of the processing of the middle substrate and the processing of the lower substrate may include forming an aligning mark for using the aligning mark as an aligning reference in the stacking and bonding of the lower substrate and the middle substrate, and the cavity may be simultaneously formed with the aligning mark in at least one of the middle substrate and the lower substrate.
[0023] The preparing of the upper substrate may include preparing an SOI wafer for the upper substrate, the SOI wafer including a first silicon layer, an intervening oxide layer, and a second silicon layer that are sequentially stacked. The processing of the upper substrate may include etching the first silicon layer using the intervening oxide layer as an etch stop layer to form the pressure chambers.
[0024] The finely processing of the lower substrate finely to form the nozzles may include: forming ink introducing portions to a predetermined depth from the top surface of the lower substrate; and forming ink ejecting holes from a bottom surface of the lower substrate for communicating with the ink introducing portion.
[0025] The stacking and bonding of the lower substrate, middle substrate, and the upper substrate may be performed using SDB (silicon direct bonding).
[0026] The forming of the piezoelectric actuator may include: forming a lower electrode on the upper substrate; forming a piezoelectric layer on the lower electrode; forming an upper electrode on the piezoelectric layer; and performing polling on the piezoelectric layer by applying an electric field to the piezoelectric layer to activate a piezoelectric characteristic of the piezoelectric layer.
[0027] The present invention thus provides a piezoelectric inkjet printhead that includes a damping membrane formed under a manifold to dampen a sudden pressure change inside the manifold for preventing cross-talk when ink is ejected, and a method of manufacturing the piezoelectric inkjet printhead.
[0028] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
FIG. 1 is a schematic sectional view showing a structure of a conventional piezoelectric inkjet printhead;
FIG. 2 is an exploded perspective view showing a specific example of a conventional piezoelectric printhead;
FIG. 3 is a vertical sectional view of the piezoelectric inkjet printhead depicted in FIG. 2;
FIG. 4 shows a speed of ink ejected through a single nozzle in comparison with a velocityspeed of ink ejected through a plurality of nozzles in the piezoelectric inkjet printhead depicted in FIGS. 2 and 3;
FIG. 5 is an exploded cut-away view of a piezoelectric inkjet printhead according to an embodiment of the present invention;
FIG. 6 is a sectional view taken along line A-A' of FIG. 5;
FIG. 7 is a sectional view taken along line B-B' of FIG. 6;
FIGS. 8A through 8C are partial vertical sectional views showing examples of a cavity of the piezoelectric inkjet printhead depicted in FIG. 6 according to another embodiments of the present invention;
FIGS. 9A through 9D are sectional views showing a process of forming alignment marks in a top surface and a bottom surface of an upper substrate in a method of manufacturing the piezoelectric inkjet printhead depicted in FIG. 6 according to an embodiment of the present invention;
FIGS. 10A through 10D are sectional views showing a process of forming pressure chambers and an ink inlet in an upper substrate, according to an embodiment of the present invention;
FIGS. 11A through 11J are sectional views showing a process of forming restrictors, a manifold, and dampers in a middle substrate, according to an embodiment of the present invention;
FIGS. 12A through 12C are sectional views showing a process of forming a damping membrane and a cavity in a middle substrate, according to an embodiment of the present invention;
FIG. 13 is a perspective view showing the cavity formed on a bottom of the middle substrate in the process depicted in FIGS. 12A through 12C;
FIGS. 14A through 14G are sectional views showing a process of forming nozzles in a lower substrate, according to an embodiment of the present invention;
FIG. 15 is a sectional view showing a process of sequentially stacking and bonding a lower substrate, a middle substrate, and an upper substrate, according to an embodiment of the present invention; and
FIG. 16 is a sectional view showing a process of forming piezoelectric actuators on an upper substrate of a piezoelectric inkjet printhead according to an embodiment of the present invention.
[0029] The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, like reference numerals denote like elements, and the thicknesses of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being "on" another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present.
[0030] FIG. 5 is a partial exploded perspective view of a piezoelectric inkjet printhead according to an embodiment of the present invention, FIG. 6 is a sectional view taken along line A-A' of FIG. 5, and FIG. 7 is a sectional view taken along line B-B' of FIG. 6.
[0031] Referring to FIGS. 5 through 7, the piezoelectric inkjet printhead of the present invention includes three substrates: an upper substrate 100, a middle substrate 200, and a lower substrate 300 that are joined together. An Ink ink passage is formed in the three substrates 100, 200, and 300, and piezoelectric actuators 190 are formed on a top surface of the upper substrate 100 for generating driving forces to eject ink.
[0032] Each of the three substrates 100, 200, and 300 is formed of a single crystal silicon wafer. Therefore, elements of the ink passage can be formed more minutely, precisely, and easily by using micromachining technologies such as photolithography and etching.
[0033] The ink passage includes an ink inlet 110 allowing inflow of ink from an ink reservoir (not shown), a plurality of ink chambers 120 containing the ink to be ejected and capable of being deformed for generating pressure variations, a manifold 210 as a common passage for distributing the ink coming through the inlet 110 to the respective ink chambers 120, restrictors 220 as individual passages for supplying the ink from the manifold 210 to the respective pressure chambers 120, and nozzles 310 through which the ink contained in the pressure chambers 120 is ejected. A damper 230 may be formed between the pressure chamber 120 and the nozzle 310 for concentrating a pressure generated in the pressure chamber 120 by the actuator 190 toward the nozzle 310 and absorbing a sudden change of the pressure. These elements of the ink passage are distributed to the three substrates 100, 200, and 300.
[0034] Specifically, the upper substrate 100 includes the ink inlet 110 and the plurality of pressure chambers 120. The ink inlet 110 penetrates the upper substrate 100 in a vertical direction and connected to an end of the manifold 210 formed in the middle substrate 200. Alternatively, two ink inlets 110 can be formed in connection with both ends of the manifold 210. The plurality of pressure chambers 120 are formed in a bottom of the upper substrate 100 and have a rectangular shape longer than the width of the manifold 210. The plurality of pressure chambers 120 are arranged in two lines along both sides of the manifold 210 formed in the middle substrate 200. Alternatively, the plurality of pressure chambers 120 can be arranged in a line along one side of the manifold 210.
[0035] The upper substrate 100 is formed of a single crystal silicon wafer that is widely used for manufacturing a semiconductor integrated circuit. The upper substrate 100 may be formed of a silicon-on-insulator (SOI) wafer. The SOI wafer usually has a stacked structure with a first silicon layer 101, an intervening oxide layer 102 formed on the first silicon layer 101, and a second silicon layer 103 bonded to the intervening oxide layer 102. The first silicon layer 101 is formed of single crystal silicon and has a thickness of about 100 µm to about 250 µm. The intervening oxide layer 102 may be formed by oxidizing the top surface of the first silicon layer 101. The intervening oxide layer 102 has a thickness of about 2 µm. The second silicon layer 103 is also formed of single crystal silicon and has a thickness of about 10 µm to about 20 µm. By using the SOI wafer for forming the upper substrate 100, the depth of the pressure chambers can be precisely adjusted. That is, when the pressure chambers 120 are formed, the intervening oxide layer 102 of the SOI wafer functions as an etch stop layer, such that the depth of the pressure chambers 120 can be determined by the thickness of the first silicon layer 101. Further, the second silicon layer 103 forming upper walls of the pressure chambers 120 is bendable according to the operations of the piezoelectric actuators 190. That is, the second silicon layer 103 operates as a vibrating plate to change the volumes of the pressure chambers 120. The thickness of the vibrating plate is determined by the thickness of the second silicon layer 103.
[0036] The piezoelectric actuators 190 are formed on the upper substrate 100. A silicon oxide layer 180 may be formed between the upper substrate 100 and the piezoelectric actuators 190. The silicon oxide layer 180 is used as an insulating layer. Further, the silicon oxide layer 180 is used to prevent diffusion and thermal stress between the upper substrate 100 and the piezoelectric actuators 190. Each of the piezoelectric actuators 190 includes a lower electrode 191 used as a common electrode, a piezoelectric layer 192 capable of deforming according to an applied voltage, and an upper electrode 193 as a driving electrode. The lower electrode 191 is formed on the entire surface of the silicon oxide layer 180. Though the lower electrode 191 can be configured with a single conductive metal layer, it may be configured with two thin metal layers formed of titanium (Ti) and platinum (Pt). The lower electrode 191 used as a common electrode and a diffusion barrier layer for preventing inter-diffusion between the piezoelectric layers 192 and the upper substrate 100. The piezoelectric layers 192 are formed on the lower electrode 191 above the respective pressure chambers 120. The piezoelectric layers 192 may be formed of a piezoelectric material such as lead zirconate titanate (PZT) ceramic. When a voltage is applied to the piezoelectric layer 192, the piezoelectric layer 192 is deformed to bend the second silicon layer 103 of the upper substrate 100 that forms the upper wall (vibrating plate) of the pressure chamber 120. The upper electrode 193 is formed on the piezoelectric layer 192 as a driving electrode for applying a voltage to the piezoelectric layer 192.
[0037] The middle substrate 200 is formed of a single crystal silicon wafer that is widely used for manufacturing a semiconductor integrated circuit. The middle substrate 200 has a thickness of about 200 µm to about 300 µm. The middle substrate 200 includes the manifold 210 connected with the ink inlet 110 and the plurality of restrictors 220 connected between the manifold and ends of the plurality of pressure chambers 120. The middle substrate 200 may include the plurality of dampers 230 connecting the plurality of pressure chambers 120 to the plurality of nozzles 310 (described in detail later) formed in the lower substrate 300. The middle substrate 200 further includes a damping membrane 214 formed under the manifold 210 and a cavity 216 formed under the damping membrane 214.
[0038] Specifically, the manifold 210 is defined in the top surface of the middle substrate 200 to a predetermined depth. The manifold 210 is elongated in one direction. As described above, in the case where the plurality of pressure chambers 120 are arranged in two lines along both sides of the manifolds 210, a long barrier rib 212 may be formed in the manifold 210 in a length direction of the manifold 210 to divide the manifold 210 into right and left portions. The barrier rib 212 effectively prevents cross-talk between the two pressure chamber lines arranged along the both sides of the manifold 210.
[0039] The damping membrane 214 is formed under the manifold 210 to dampen sudden pressure variations of the manifold 210. The thickness of the damping membrane 214 may range from about 10 µm to about 20 µm. If the damping membrane 214 is too thick, the damping membrane is not easily deformed, and if the damping membrane 214 is too thin, the damping membrane 214 is easily damaged or broken.
[0040] The cavity 216 is formed under the damping membrane 214 to allow free deformation of the damping membranes 214. The cavity 216 may have substantially the same width as the manifold 210 formed on the damping membrane 214. A supporting rib 217 may be formed in the cavity 216 in correspondence with the barrier rib 212. The supporting rib 217 supports the damping membrane 214 to prevent excessive deformation and breakage of the damping membrane 214.
[0041] Since the damping membrane 214 is covered by the lower substrate 300 bonded to the middle substrate 200, the damping membrane 214 is not exposed to the outside. Therefore, the damping membrane 214 can be prevented from breakage due to contact with an external object.
[0042] Further, the cavity 216, as shown in FIG. 7, may extend to an edge of the middle substrate 200 for communicating with the outside. On the contrary, if the cavity 216 is closed, the free deformation of the damping membrane 214 may be hindered by the pressure of the closed cavity 216. Further, in the case where the cavity 216 is opened to the outside, gas generated during the boding process of the middle substrate 200 and the lower substrate 300 can be easily discharged to the outside through the cavity 216, such that the formation of voids between the middle substrate 200 and the lower substrate 300 can be prevented. This will be more fully described when presenting a method of manufacturing the piezoelectric inkjet printhead is described.
[0043] As described above, according to the present invention, the damping membrane 214 formed under the manifold 210 dampens a sudden pressure change in the manifold 210, so that cross-talk can be effectively prevented between the plurality of pressure chambers 120 arranged in a line along a side of the manifold 210. Therefore, ink can be uniformly ejected through the plurality of nozzles 310, and thus, printing quality can be improved.
[0044] Each of the plurality of restrictors 220 is formed in the top surface of the middle substrate 200 to a predetermined depth (e.g., about 20 µm to 40 µm).
One end of the restrictor 220 is connected to the manifold 210, and the other end of the restrictor 220 to one end of the pressure chamber 120. The restrictor 220 controls ink flow from the manifold 210 to the pressure chamber 120, such that ink can be supplied to the pressure chamber 210 at a proper rate. Further, when the ink is ejected, the restrictor 220 prevents the ink from reversely flowing from the pressure chamber 120 to the manifold 210. Meanwhile, the restrictor 220 can be formed to have the same depth as the manifold 210. Each of the dampers 230 is vertically defined through the middle substrate 200 at a position corresponding to the other end of each pressure chamber 120.
[0045] The lower substrate 300 includes the plurality of nozzles 310 to eject ink. The lower substrate 300 is formed of a single crystal silicon wafer that is widely used for manufacturing a semiconductor integrated circuit, and has a thickness of about 100 µm to about 200 µm.
[0046] Each of the plurality of nozzles 310 is vertically formed through the lower substrate 300 at a position corresponding to the damper 230. The nozzle 310 may include an ink introducing portion 311 formed in an upper portion of the lower substrate 300 and an ink ejecting hole 312 formed in a lower portion of the lower substrate 300 for ejecting ink therethrough. The ink ejecting hole 312 may be a vertical hole having a uniform diameter, and the ink introducing portion 311 may have a pyramid shape with a gradually decreasing cross-section from the damper 230 to the ink ejecting hole 312.
[0047] As described above, the three substrates 100, 200, and 300 are stacked and bonded together, thereby forming the piezoelectric inkjet printhead of the present invention. The ink passage in the three substrates 100, 200, and 300 is formed by the sequential connection of the ink inlet 110, the manifold 210, the pressure chambers 120, the dampers 230, and the nozzles 310.
[0048] FIGS. 8A through 8C are partial vertical sectional views showing examples of the cavity 216 formed in the piezoelectric inkjet printhead depicted in FIG. 6, according to an embodiment of the present invention.
[0049] Referring to FIG. 8A, a the cavity 216 can be formed to have a width larger than that of the manifold 210. In this case, gas generated when the middle substrate 200 and the lower substrate 300 are bonded can be more easily collected and discharged through the cavity 216.
[0050] Referring to FIG. 8B, a the cavity 216 can be formed in the top surface of the lower substrate 300 to a predetermined depth instead of being formed in the bottom surface of the middle substrate 200. In this case, the a supporting rib 217 is also formed on the top surface of the lower substrate 300. When the manifold has a comparatively large depth and the lower substrate 300 has a comparatively large thickness, the cavity 216 shown in FIG. 8B may be suitable.
[0051] Referring to FIG. 8C, a the cavity 216 can be formed in the bottom surface of the middle substrate 200 and the top surface of the lower substrate 300. In this case, a the supporting rib 217 is also formed on the bottom surface of the middle substrate 200 and the top surface of the lower substrate 300. When a cavity cannot be formed in the bottom surface of the middle substrate 200 to a sufficient depth, the cavity 216 shown in FIG. 8C may be suitable.
[0052] As described above, at least one of the bottom surface of the middle substrate 200 and the top surface of the lower substrate 300 may be formed with the cavity 216 depending on the depth of the manifold 210 and the thicknesses of the middle substrate 200 and the lower substrate 300.
[0053] An operation of the piezoelectric inkjet printhead having the above-described structure will now be described according to the present invention.
[0054] Ink drawn into the manifold 210 from the ink reservoir (not shown) is supplied to the respective pressure chambers 120 through the plurality of restrictors 220. When the pressure chamber 120 is filled with the ink and a voltage is applied to the piezoelectric layer 192 through the upper electrode 193 of the piezoelectric actuator 190, the piezoelectric layer 192 is deformed to bend down the second silicon layer 103 (vibrating plate) of the upper substrate 100.
The volume of the pressure chamber 120 decreases as the second silicon layer 103 is bent down, and thus the pressure of the pressure chamber 120 increases, such that the ink contained in the pressure chamber 120 can be ejected to the outside through the damper 230 and the nozzle 310.
[0055] When the voltage applied to the piezoelectric layer 192 of the piezoelectric actuator 190 is cut off, the piezoelectric layer 192 returns to its original shape, and as a result the second silicon layer 103 (vibrating layer) also returns to its original shape to increase the volume of the pressure chamber 120. As the volume of the pressure chamber 120 increases, the pressure of the pressure chamber 120 decreases, such that ink can be drawn into the pressure chamber 120 from the manifold 210 through the restrictor 220.
[0056] In this process, the pressure inside the manifold 210 changes very rapidly. However, according to the present invention, the damping membrane 214 is provided under the manifold 210 to dampen the rapid pressure change of the manifold 210. Therefore, when ink is ejected, cross-talk can be effectively prevented and the ink can be uniformed ejected through the plurality of nozzles at awith constant performance, thereby improving printing quality of the piezoelectric inkjet printhead of the present invention.
[0057] A method of manufacturing the piezoelectric inkjet printhead having the above-mentioned structure will now be described according to an embodiment of the present invention.
[0058] To put it bBriefly, the upper substrate, the middle substrate, and the lower substrate in which the elements forming the ink passage are included are individually fabricated, and then the three substrates are stacked and bonded together. After that, the piezoelectric actuators are formed on the upper substrate, thereby completely manufacturing the piezoelectric inkjet printhead of the present invention. Meanwhile, the upper substrate, the middle substrate, and the lower substrate may be fabricated in no particular order. That is, the lower substrate or the middle substrate may be fabricated prior to other substrates, or two or three substrates may be fabricated at the same time. However, fabrication of the respective substrates will now be described in the upper, middle, and lower substrate order as an example.
[0059] FIGS. 9A through 9D are sectional views showing a process of forming alignment marks in a top surface and a bottom surface of an upper substrate in a method of manufacturing the piezoelectric inkjet printhead depicted in FIG. 6 according to an embodiment of the present invention.
[0060] Referring to FIG. 9A, an upper substrate 100 is formed of a single crystal silicon wafer according to the current embodiment of the present invention. Since the single crystal silicon wafer, which is widely used for manufacturing a semiconductor device, can be directly used, it is advantageous for the mass production of the upper substrate 100. Further, the upper substrate 100 may be formed of an SOI wafer for precisely forming the pressure chamber 120 (refer to FIG. 120) at a predetermined depth. The SOI wafer, as described above, has a stacked structure with a first silicon layer 101, an intervening oxide layer 102 formed on the first silicon layer 101, and a second silicon layer 103 bonded to the intervening oxide layer 102.
[0061] An upper substrate 100 having a first silicon layer 101 with a thickness of about 650 µm, an intervening oxide layer 102 with a thickness of about 2 µm, and a second silicon layer 103 with a thickness of about 10 µm to 20 µm is prepared. The thickness of the first silicon layer 101 of the upper substrate 100 is decreased by chemical-mechanical polishing (CMP), and then the entire surface of the upper substrate 100 is cleaned. Here, the thickness of the first silicon layer 101 may be reduced to a proper thickness in accordance with the thickness of the pressure chamber 120 to be formed. For example, the thickness of the first silicon layer 101 may be reduced to a thickness ranging from about 100 µm to about 250 µm. Further, the upper substrate 100 may be cleaned by an organic cleaning method using acetone, isopropyl alcohol, etc., or an acid cleaning method using sulfuric acid, buffered oxide etchant (BOE), etc, or an SC1 cleaning method.
[0062] After the cleaning, the upper substrate 100 is wet and dry oxidized to form silicon oxide layers 151 a and 151 b on top and bottom surfaces. The silicon oxide layers 151 a and 151 b have a thickness of about 5,000 Å to about 15,000 Å .
[0063] Referring to FIG. 9B, a photoresist PR1 is formed on the silicon layer 151 a formed on the top surface of the upper substrate 100. Next, openings 148 in which aligning marks 141 (refer to FIG. 9C) will be formed are formed on the photoresist PR1 by patterning the photoresist PR1. The patterning of the photoresist PR1 may be performed using a well-known photolithography method including exposing and developing. Other photoresist described below may be patterned using the same method.
[0064] Referring to FIG. 9C, the silicon oxide layer 151 a is etched using the patterned photoresist PR1 as an etch mask to remove exposed portions of the silicon oxide layer 151a by the patterned photoresist PR1. Consecutively, the upper substrate 100 is etched by a predetermined depth to form the aligning marks 141. Here, the etching of the silicon oxide layer 151 a may be performed by a dry etching method such as reactive ion etching (RIE) or a wet etching method using BOE. The etching of the upper substrate 100 may be performed by a dry etching method such as RIE using inductively coupled plasma (ICP), or a wet etching method using silicon etchant such as tetramethyl ammonium hydroxide (TMAH) or KOH.
[0065] Next, the photoresist PR1 is removed using the organic cleaning method or the acid cleaning method described above. Alternatively, the photoresist PR1 may be removed by ashing. Other photoresist described below may be removed using the same method.
[0066] Although the photoresist PR1 is removed after the silicon oxide layer 151 a and the upper substrate 100 are etched, the photoresist PR1 can be removed after the silicon oxide layer 151 a is etched using the photoresist PR1 as an etch mask, and then the upper substrate 100 can be etched using the etched silicon oxide layer 151 a as an etch mask.
[0067] Referring to FIG. 9D, aligning marks 142 are formed on the bottom surface of the upper substrate 100 according to the same method described above.
[0068] FIGS. 10A through 10D are sectional views showing a process of forming a pressure chamber and an ink inlet in the upper substrate 100.
[0069] Referring to FIG. 10A, a photoresist PR2 is formed on the silicon oxide layer 151 b formed on the bottom surface of the upper substrate 100, and consecutively the photoresist PR2 is patterned to define openings 128 for forming pressure chambers 120 (refer to FIG. 10C) and an opening (not shown) for forming an ink inlet (refer to 110 in FIG. 5).
[0070] Referring to FIG. 10B, the photoresist PR2 is used as an etch mask to etch the silicon oxide layer 151b by a dry etching method such as RIE or a wet etching method using BOE in order to remove portions of the silicon oxide layer 151 b exposed by the openings 128. As a result, the bottom surface of the upper substrate 100 is partially exposed.
[0071] Referring to FIG. 10C, the exposed portions of the upper substrate 100 is etched to a predetermined depth using the photoresist PR2 as an etch mask, thereby forming pressure chambers 120. At this time, an ink inlet 110 is partially formed in the upper substrate 100. The etching of the upper substrate 100 may be performed by a dry etching method such as RIE using inductively coupled plasma (ICP).
[0072] In the case where the upper substrate 100 is formed of an SOI wafer as shown, the intervening oxide layer 102 of the SOI wafer functions as an etch stop layer, such that only the first silicon layer 101 can be etched. Therefore, the pressure chambers 120 can be precisely formed at a desired depth by adjusting the thickness of the first silicon layer 101. The thickness of the first silicon layer 101 can be easily adjusted in the chemical-mechanical polishing (CMP) process. Meanwhile, the second silicon layer 103 forms the upper wall of the pressure chambers 120 and functions as a vibrating plate as described above, and the thickness of the second silicon layer 103 can be easily adjusted in the same manner by the CMP.
[0073] Referring to FIG. 10D, the photoresist PR2 is removed by the method described above, thereby forming the pressure chambers 120 and the ink inlet 110 (not shown) in the bottom surface of the upper substrate 100. The ink inlet 110 will be post-processed in a last process to vertically pass through the upper substrate 100 (described later).
[0074] As described above, the upper substrate 100 is dry etched using the photoresist PR2 as an etch mask and then the photoresist PR2 is removed. However, the upper substrate 100 can be dry etched using the silicon oxide layer 151 b as an etch mask after the photoresist PR2 is removed.
[0075] FIGS. 11A through 11J are sectional views showing a process of forming restrictors, a manifold, and dampers in the middle substrate 200.
[0076] Referring to FIG. 11A, a middle substrate 200 is formed of a single crystal silicon wafer. First, a silicon wafer is chemical-mechanical polished to prepare the middle substrate 200 with a thickness of about 200 µm to about 300 µm. The thickness of the middle substrate 200 may be determined according to the depth of a manifold 210 (refer to FIG. 5) to be formed in a top surface of the middle substrate 200.
[0077] The middle substrate 200 is wet and dry oxidized to form silicon oxide layers 251 a and 251 b on a top surface and a bottom surface of the middle substrate 200 to a thickness of about 5,000 Å to about 15,000 Å .
[0078] Referring to FIG. 11B, a photoresist PR3 is formed on the silicon layer 251 a formed on the top surface of the middle substrate 200. Next, the photoresist PR3 is patterned to define openings 228 for forming restrictors 220 (refer to FIG. 5) in the top surface of the middle substrate 200, and to define openings 248 for forming aligning marks. Although the aligning marks can be formed before the restrictors 220 are formed, the aligning marks are simultaneously formed with the restrictors 220 to reduce manufacturing processes (described later).
[0079] Referring to FIG. 11C, the patterned photoresist PR3 is used as an etch mask to etch portions of the silicon layer 251 a exposed by the openings 228 and 248, and consecutively the middle substrate 200 is etched to a predetermined depth (for example, about 20 µm to 40 µm) to form the restrictors 220 and aligning marks 241. Here, the silicon oxide layer 251 a and the middle substrate 200 may be etched using the dry etching method or the wet etching method described above.
[0080] The photoresist PR3 is removed using the above-described method. The photoresist PR3 may be removed after the silicon oxide layer 251 a is etched. In this case, the silicon layer 251 a is used as an etch mask for etching the middle substrate 200.
[0081] Referring to FIG. 11 D, after the middle substrate 200 is cleaned using the above-described cleaning method, the middle substrate 200 is wet and dry oxidized to form silicon oxide layers 251 a and 251 b on the top and bottom surfaces of the middle substrate 200 again. Therefore, the silicon layer can be formed inside the restrictors 220 and the aligning marks 241.
[0082] Referring to FIG. 11 E, a photoresist PR4 is formed on the silicon oxide layer 251 a formed on the top surface of the middle substrate 200, and the photoresist PR4 is patterned such that an opening 218 (refer to FIG. 11 F) for the manifold 210 (refer to FIG. 5) is formed on the top surface of the middle substrate 200. In the case where the barrier rib 212 (refer to FIG. 5) is formed in the manifold 210, a portion of the photoresist PR4 corresponding to the barrier rib 212 is not removed.
[0083] Referring to FIG. 11 F, the silicon oxide layer 251 a exposed by the opening 218 is etched by the above-described wet or dry etching method using the photoresist PR4 as an etch mask to partially expose the top surface of the middle substrate 200. After that, the photoresist PR4 is removed by the above-described method.
[0084] Referring to FIG. 11 G, a photoresist PR5 is formed on the silicon oxide layer 251 a formed on the top surface of the middle substrate 200. Here, the photoresist PR5 is also formed on the exposed top surface of the middle substrate 200. Then, the photoresist PR5 is patterned to form openings 238 for the dampers 230 (refer to FIG. 5).
[0085] Referring to FIG. 11 H, the silicon oxide layer 251 a exposed by the openings 238 is etched by the above-described dry or wet etching method using the photoresist PR5 as an etch mask to partially expose the top surface of the middle substrate 200. Consecutively, the exposed top surface of the middle substrate 200 is etched to a predetermined depth to form dampers 230 partially. Here, the etched depth is determined depending on the difference between the thickness of the middle substrate 200 and the depth of the manifold 210. The etching of the middle substrate 200 may be performed by a dry etching method such as RIE using ICP.
[0086] Referring to FIG. 11I, the photoresist PR5 is removed by the above-described method to expose a portion of the top surface of the middle substrate 200 for forming the manifold 210.
[0087] Referring to FIG. 11J, the exposed top surface portion of the middle substrate 200 and bottoms of the partially-formed dampers 230 are etched using the silicon oxide layer 251 a as an etch mask to form a manifold 210 and the dampers 230. Here, the dampers 230 pass through the middle substrate 200 in a vertical direction, and the manifold 210 is formed to a predetermined depth from the top surface of the middle substrate 200. Further, a barrier rib 212 is formed in the manifold 210 to divide the manifold 210 into right and left portions. The etching of the middle substrate 200 may also be performed by the dry etching method such as RIE using ICP.
[0088] FIGS. 12A through 12C are sectional views showing a process of forming a damping membrane and a cavity in the middle substrate 200.
[0089] Referring to FIG. 12A, a photoresist PR6 is formed on the silicon oxide layer 251 b formed on the bottom surface of the middle substrate 200. Next, the photoresist PR6 is patterned such that an opening 229 and openings 249 are formed on the silicon oxide layer 251 b for the cavity 216 (refer to FIG. 5) and aligning marks. In the case where the supporting rib 217 (refer to FIG. 5) is formed in the cavity 216, a portion of the photoresist PR6 corresponding to the supporting rib 217 is not removed when the photoresist PR6 is patterned.
[0090] Referring to FIG. 12B, the silicon oxide layer 251b exposed by the openings 229 and 249 is etched using the photoresist PR6 as an etch mask, and the bottom surface of the middle substrate 200 is etched to a predetermined depth to form a cavity 216 and aligning marks 242. Consequently, a damping membrane 214 is formed between the cavity 216 and the manifold 210, and a supporting rib 217 is formed in the cavity 216. Here, the damping membrane 214 formed under the manifold 210 by the etching has a thickness of about 10 µm to about 20 µm. The silicon oxide layer 251 b may be etched by the above-described dry or wet etching method, and the middle substrate 200 may be etched by the dry etching method.
[0091] Thereafter, the photoresist PR6 is removed by the above-described method. The photoresist PR6 may be removed after the silicon oxide layer 251 b is etched. In this case, the silicon oxide layer 251 b is used as an etch mask for etching the middle substrate 200.
[0092] Referring to FIG. 12C, the remaining silicon oxide layers 251 a and 251 b are removed by wet etching, completely forming the middle substrate 200 with the damping membrane 214 and the cavity 216.
[0093] As described above, according to the present invention, the cavity 216 and the damping membrane 214 are formed in the bottom surface of the middle substrate 200 together with the aligning marks 242. Therefore, an additional process is not required to form the cavity 216 and the damping membrane 214.
[0094] Meanwhile, the cavity 216 and the damping membrane 214 can be formed in the bottom surface of the middle substrate 200 before the restrictors 220, the manifold 210, and the dampers 230 are formed in the top surface of the middle substrate 200.
[0095] The cavity 216 may have substantially the same width as the manifold 210 as shown in FIG. 6, or a larger width than the manifold 210 as shown in FIG. 8A.
[0096] Further, the cavity 216 can be formed in the top surface of the lower substrate 300 to a predetermined depth as shown in FIG. 8B. In this case, the cavity 216 may be formed in the top surface of the lower substrate 300 together with aligning marks 341.
[0097] Furthermore, as shown in FIG. 8C, the cavity 216 can be formed in the bottom surface of the middle substrate 200 and the top surface of the lower substrate 300.
[0098] FIG. 13 is a perspective view showing the cavity 216 formed on the bottom of the middle substrate 200 in the process depicted in FIGS. 12A through 12C.
[0099] Referring to FIG. 13, the inkjet printhead of the present invention is formed using silicon wafers in the form of a number of chips. Therefore, the cavity 216 may be formed to extend to the edge of a silicon wafer for the middle substrate 200 in the process shown in FIGS. 12A through 12C. In this case, gas generating generated when the middle substrate 200 and the lower substrate 300 are bonded can be easily discharged to the outside through the cavity 216. This will be more fully described when presenting the bonding process is described.
[0100] FIGS. 14A through 14G are sectional views showing a process of forming nozzles in a lower substrate, according to an embodiment of the present invention.
[0101] Referring to FIG. 14A, a lower substrate 300 is formed of a single crystal silicon wafer according to an embodiment of the present invention. First, a silicon wafer is chemical-mechanical polished to a thickness of about 100 µm to about 200 µm for the lower substrate 300.
[0102] The lower substrate 300 is wet and dry oxidized to form silicon oxide layers 351a and 351b on a top surface and a bottom surface of the lower substrate 300 to a thickness of about 5,000 Å to 15,000 Å . Then, aligning marks 341 and 342 may be formed on the top and bottom surface of the lower substrate 300. The aligning marks 341 and 342 may be formed by the same method shown in FIGS. 9A through 9D.
[0103] Referring to FIG. 14B, a photoresist PR7 is formed on the silicon layer 351 a formed on the top surface of the lower substrate 300, and the photoresist PR7 is patterned to form openings 318 on the top surface of the lower substrate 300 for the ink introducing portions 311 (refer to FIG. 5) of the nozzles 310 (refer to FIG. 5).
[0104] Referring to 14C, the photoresist PR7 is used as an etch mask to etch the silicon oxide layer 351 a exposed by the openings 318 to partially expose the top surface of the lower substrate 300. Here, the etching of the silicon oxide layer 351 a may be performed by the dry or wet etching as described above. Then, the photoresist PR7 is removed, and the lower substrate 300 is cleaned by an acid cleaning method using sulfuric acid, BOE, etc.
[0105] Referring to FIG. 14D, the exposed top surface of the lower substrate 300 is etched to a predetermined depth using the silicon oxide layer 351 a as an etch mask, thereby forming an ink introducing portions 311 of nozzles. The etching of the lower substrate 300 may be performed by a wet etching method using silicon etchant such as TMAH or KOH. In this case, the ink introducing portions 311 may be formed into a pyramid shape by the anisotropic wet etching characteristic of the lower substrate 300 (etching along the crystal planes in the lower substrate 300).
[0106] Referring to FIG. 14E, a photoresist PR8 is formed on the silicon oxide layer 351 b formed on the bottom surface of the lower substrate 300, and the photoresist PR8 is patterned to form openings 319 on the bottom surface of the lower substrate 300 for the ink ejecting holes 312 (refer to FIG. 5) of the nozzles.
[0107] Referring to FIG. 14F, the silicon oxide layer 351 b exposed by the openings 319 is wet or dry etched using the photoresist PR8 as an etch mask to partially expose the bottom surface of lower substrate 300, and then the photoresist PR8 is removed.
[0108] Referring to FIG. 14G, the exposed bottom surface of the lower substrate 300 is etched using the silicon oxide layer 351 b as an etch mask until the lower substrate 300 is penetrated, thereby forming ink ejecting holes 312 communicating with the ink introducing portions 311. Here, the etching of the lower substrate 300 may be performed by a dry etching method such as RIE using ICP.
[0109] In this way, the lower substrate 300 can be completely formed with the nozzles 310 having the ink introducing portions 311 and the ink ejecting holes 312.
[0110] FIG. 15 is a sectional view showing a process of sequentially stacking and bonding the lower substrate 300, the middle substrate 200, and the upper substrate 100, according to an embodiment of the present invention.
[0111] Referring to FIG. 15, the lower substrate 300, the middle substrate 200, and the upper substrate 100 that are formed as described above are sequentially stacked and bonded together. Here, if the aligning marks 141, 142, 241, 242, 341, 342 of the three substrates 100, 200, and 300 are used, the three substrates 100, 200, and 300 can be aligned more precisely. Further, the three substrates 100, 200, and 300 may be bonded together by well-known silicon direct bonding (SDB).
[0112] Generally, in the SDB, silicon wafers to be bonded are cleaned first. By the cleaning, thin layers having ions and molecules such as OH-, H+, H2O, H2, O2 are formed on the surfaces of the silicon wafers. Next, the silicon wafers are brought into contact with each other by pressure to pre-bond the silicon wafers by the Van Der Waals's force between the ions and molecules. Next, the pre-bonded silicon wafers are heated to a temperature of about 100 °C in a heat treatment furnace to bond the silicon wafers strongly by the interdiffusion of atoms between the silicon wafers. During the heat treatment, gas is generated by the ions and molecules of the silicon wafers.
[0113] However, according to the present invention, the gas generated during the bonding process of the middle substrate 200 and the lower substrate 300 can be easily discharged through the cavity 216 since the cavity 216 extends to the edge of the middle substrate 200 as shown in FIG. 13. Therefore, voids resulting from the gas can be prevented or minimized between the middle substrate 200 and the lower substrate 300.
[0114] FIG. 16 is a sectional view showing a process of forming a piezoelectric actuator on the upper substrate 100 of the piezoelectric inkjet printhead according to the present invention, according to an embodiment of the present invention.
[0115] Referring to FIG. 16, in a state where the lower substrate 300, the middle substrate 200, and the upper substrate 100 are sequentially stacked and bonded together, a silicon oxide layer 180 is formed on the top surface of the upper substrate 100 as an insulating layer. However, since the silicon oxide layer 151 a is already formed on the top surface of the upper substrate 100 when the upper substrate 100 is formed, the silicon oxide layer 151a may be used as the silicon oxide layer 180 instead of forming the silicon oxide layer 180.
[0116] Next, a lower electrode 191 of piezoelectric actuators is formed on the silicon oxide layer 180. The lower electrode 191 may include two thin metal layers formed of titanium (Ti) and platinum (Pt). In this case, the lower electrode 191 may be formed by sputtering titanium (Ti) and platinum (Pt) onto the entire surface of the silicon oxide layer 180 to a predetermined thickness.
[0117] Next, piezoelectric layers 192 and upper electrodes 193 are formed on the lower electrode 191. Specifically, piezoelectric paste is applied to the lower electrode 191 above the pressure chambers 120 to a predetermined thickness by using a screen printing method, and it is dried for a predetermined time to form the piezoelectric layers 192. Various piezoelectric materials can be used for the piezoelectric layers 192. Generally, PZT ceramic may be used for the piezoelectric layers 192. Thereafter, an electrode material such as Ag-Pd paste is printed on the dried piezoelectric layers 192 to form the upper electrodes 193. Next, the piezoelectric layers 192 and the upper electrodes 193 are sintered at a predetermined temperature of, for example, 900 to 1,000 °C. Then, an electric field is applied to the piezoelectric layers 192 to activate the piezoelectric characteristic of the piezoelectric layers 192 (polling treatment). In this way, piezoelectric actuators 190 having the lower electrode 191, the piezoelectric layers 192, and the upper electrodes 193 are formed on the upper substrate 100.
[0118] Then, the ink inlet 110 (refer to FIG. 5), which is partially formed in the bottom surface of the upper substrate 100 to a predetermined depth when the pressure chambers 120 are formed in the bottom surface of the upper substrate 100 in the process shown in FIG. 10A through 10D, is post-processed to pass through the upper substrate 100. For example, a thin portion of the upper substrate 100 located above the ink inlet 110 can be removed using an adhesive tape to allow the ink inlet 110 to pass through the upper substrate 100.
[0120] As described above, according to the present invention, the damping membrane is formed under the manifold to dampen a sudden pressure change inside the manifold, so that cross-talk can be effectively prevented when ink is ejected. Therefore, ink can be uniformly ejected through a number of nozzles, and thereby printing quality can be improved.
[0121] Further, the damping membrane is protected by the lower substrate and is not exposed to the outside, so that the damping membrane can be prevented from being damaged or broken by external objects.
[0122] Furthermore, gas generating generated when the substrates are bonded can be smoothly discharged to the outside through the cavity formed under the damping membrane, so that voids generating between the substrates by the gas can be prevented. Therefore, defective products can be reduced and yield can be increased in manufacturing the piezoelectric inkjet printhead.
[0123] In addition, the damping membrane and the cavity are formed together with the aligning marks in the bottom surface of the middle substrate, so that an additional process is not required for the damping membrane and the cavity.
[0124] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention. For example, the processes described for elements of the printhead of the present invention are exemplary ones, and thus various other processes including etching can be applied to the present invention. Further, the process or procedures can be performed in a different order. Therefore, the scope of the present invention should be defined by the following claims.
1. A piezoelectric inkjet printhead comprising:
an upper substrate including an ink inlet therethrough for allowing inflow of ink and a plurality of pressure chambers in a bottom surface for containing the ink to be ejected;
a middle substrate bonded to the bottom surface of the upper substrate, the middle substrate including a manifold formed in a top surface in connection with the ink inlet, a plurality of restrictors connecting the manifold to respective one ends of the pressure chambers, and a plurality of dampers formed therethrough at positions corresponding to respective opposite ends of the pressure chambers;
a lower substrate bonded to a bottom surface of the middle substrate, the lower substrate including a plurality of nozzles formed therethrough at positions corresponding to the plurality of dampers for ejecting the ink;
an actuator formed on the upper substrate to apply a driving force to each of the pressure chambers for ejecting the ink,
wherein the middle substrate further includes a damping membrane formed under the manifold for dampening a pressure change inside the manifold, and
a cavity is defined formed in at least one of the bottom surface of the middle substrate and a top surface of the lower substrate under the damping membrane.
2. The piezoelectric inkjet printhead of claim 1, wherein the damping membrane has a
substantial thickness of about 10 µm to about 20 µm.
3. The piezoelectric inkjet printhead of claim 1 or 2, wherein the cavity extends to
an edge of the at least one of the bottom surface of the middle substrate and the
top surface of the lower substrate for communicating with an outside.
4. The piezoelectric inkjet printhead of any preceding claim, wherein the cavity has
substantially the same width as the manifold.
5. The piezoelectric inkjet printhead of any of claims 1 to 3, wherein the cavity has
a width larger than the manifold.
6. The piezoelectric inkjet printhead of any preceding claim, wherein the upper substrate
is formed of a silicon-on-insulator wafer, the silicon-on-insulator wafer including
a first silicon layer, an intervening oxide layer, and a second silicon layer that
are sequentially stacked.
7. The piezoelectric inkjet printhead of claim 6, wherein the first silicon layer is
formed with the pressure chambers and the second silicon layer is used as a vibrating
plate capable of bending by operation of the piezoelectric actuator.
8. The piezoelectric inkjet printhead of any preceding claim, wherein the manifold is
elongated in one direction, and the pressure chambers are arranged in two lines along
both sides of the manifold.
9. The piezoelectric inkjet printhead of claim 8, wherein a barrier rib is formed in
the manifold along a length direction of the manifold.
10. The piezoelectric inkjet printhead of claim 9, wherein a supporting rib is formed
in the cavity along a length direction of the cavity in correspondence with the barrier
rib.
11. The piezoelectric inkjet printhead of any preceding claim, wherein the piezoelectric
actuator comprises:
a lower electrode formed on the upper substrate;
a piezoelectric layer formed on the lower electrode above each of the pressure chambers; and
an upper electrode formed on the piezoelectric layer for applying a voltage to the piezoelectric layer.
12. The piezoelectric inkjet printhead of any preceding claim, wherein each of the nozzles
comprises:
an ink introducing portion formed to a predetermined depth from the top surface of the lower substrate; and
an ink ejecting hole formed from a bottom surface of the lower substrate for communicating with the ink introducing portion.
13. A method of manufacturing a piezoelectric inkjet printhead, comprising:
preparing an upper substrate, a middle substrate, and a lower substrate that are formed of silicon wafers;
processing the upper substrate finely to form an ink inlet allowing inflow of ink and a plurality of pressure chambers containing the ink to be ejected;
processing the middle substrate finely to form a manifold in a top surface of the middle substrate in connection with the ink inlet, a plurality of restrictors connecting the manifold to respective one ends of the pressure chambers, and a plurality of dampers through the middle substrate at positions corresponding to respective opposite ends of the pressure chambers;
processing the lower substrate finely to form a plurality of nozzles ejecting the ink therethrough;
sequentially stacking and bonding the lower substrate, the middle substrate, and the upper substrate; and
forming a piezoelectric actuator on the upper substrate, the piezoelectric actuator providing a driving force for ejecting the ink,
wherein at least one of the processing of the middle substrate and the processing of the lower substrate includes forming a cavity in at least one of a bottom surface of the middle substrate and a top surface of the lower substrate to a predetermined depth, and simultaneously forming a damping membrane between the manifold and the cavity to a predetermined thickness for dampening pressure change inside the manifold.
14. The method of claim 13, wherein the damping membrane has a substantial thickness of
about 10 µm to about 20 µm.
15. The method of claim 13 or 14, wherein the cavity extends to an edge of at least one
of the silicon wafers forming the middle substrate and the lower substrate for communicating
with an outside.
16. The method of any of claims 13 to 15, wherein the cavity has substantially the same
width as the manifold.
17. The method of any of claims 13 to 15, wherein the cavity has a width larger than the
manifold.
18. The method of any of claims 13 to 17, wherein each of the processing of the middle
substrate and the processing of the lower substrate comprises forming an aligning
mark for using the aligning mark as an aligning reference in the stacking and bonding
of the lower substrate and the middle substrate, and
the cavity is simultaneously formed with the aligning mark in at least one of the middle substrate and the lower substrate.
the cavity is simultaneously formed with the aligning mark in at least one of the middle substrate and the lower substrate.
19. The method of claim 18, wherein the forming of the cavity and the forming of the aligning
mark comprise:
forming a silicon oxide layer on at least one surface of the bottom surface of the middle substrate and the top surface of the lower substrate;
forming a photoresist on the silicon oxide layer and patterning the photoresist to form openings for the cavity and the aligning mark;
etching the silicon oxide layer exposed through the openings to expose the at least one surface; and
etching the at least one surface exposed by the etching of the silicon oxide layer to a predetermined depth to form the cavity and the aligning mark.
20. The method of any of claim 13 to 19, wherein the manifold is formed to have an elongated
shape in one direction in the processing of the middle substrate, and the pressure
chambers are formed to be arranged in two lines along both sides of the manifold in
the processing of the upper substrate.
21. The method of claim 20, wherein the processing of the middle substrate comprises forming
a barrier rib in the manifold along a length direction of the manifold.
22. The method of claim 21, wherein the forming of the cavity comprises forming a supporting
rib in the cavity along a length direction of the cavity in correspondence with the
barrier rib.
23. The method of any of claims 13 to 22, wherein the preparing of the upper substrate
comprises preparing an silicon-on-insulator wafer for the upper substrate, the silicon-on-insulator
wafer including a first silicon layer, an intervening oxide layer, and a second silicon
layer that are sequentially stacked.
24. The method of claim 23, wherein the processing of the upper substrate comprises etching
the first silicon layer using the intervening oxide layer as an etch stop layer to
form the pressure chambers.
25. The method of any of claims 13 to 24, wherein the processing of the lower substrate
finely to form the nozzles comprises:
forming ink introducing portions to a predetermined depth from the top surface of the lower substrate; and
forming ink ejecting holes from a bottom surface of the lower substrate for communicating with the ink introducing portion.
26. The method of any of claims 13 to 25, wherein the stacking and bonding of the lower
substrate, middle substrate, and the upper substrate is performed using silicon direct
bonding.
27. The method of any of claims 13 to 26, wherein the forming of the piezoelectric actuator
comprises:
forming a lower electrode on the upper substrate;
forming a piezoelectric layer on the lower electrode;
forming an upper electrode on the piezoelectric layer; and
performing polling on the piezoelectric layer by applying an electric field to the piezoelectric layer to activate a piezoelectric characteristic of the piezoelectric layer.